A still image from October 2011 video footage shows Abu Yahya al-Libi, a Libyan cleric and top Al Qaeda leader, who was killed in a US drone strike in Pakistan earlier this week, confirmed Tuesday afternoon.

While his death is confirmed, how much of a blow this will deal to Al Qaeda is contested. One American official told the Times: “Zawahri will be hard-pressed to find any one person who can readily step into Abu Yahya’s shoes. In addition to his gravitas as a longstanding member of A.Q.’s leadership, Abu Yahya’s religious credentials gave him the authority to issue fatwas, operational approvals and guidance to the core group in Pakistan and regional affiliates. There is no one who even comes close in terms of replacing the expertise A.Q. has just lost.”

Mr. Roggio acknowledges that Libi has been a top figure for the group, but writes that Al Qaeda has been able to replace other leaders killed by the US. One US intelligence official told him Al Qaeda did not rely on Libi alone. "Libi was an important member, without a doubt, but he didn't operate in a vacuum," he said, according to Roggio.

And are all these deaths in America's long-term interests? That's a thorny question right there. Libi for all his association with Al Qaeda, was probably among the moderates within the group's thinkers, reported to be an opponent of takfir – the practice of declaring all Muslims out of step with Al Qaeda's views on the faith as apostates, deserving of death – and some who follow the group believe his death may just create space for someone more extreme to climb up the ladder.

That it took almost 24 hours for the US to confirm that it was Libi who was killed in the strike indicates how limited the United States' intelligence presence is on the ground in northwest Pakistan, Bloomberg Businessweek reports, noting that it often relies on surveillance of phone calls, text messages, e-mails, and jihadist websites, which can be unreliable.

The delay in confirmation also highlights the fact that the strikes are often carried out without the US being certain that it is targeting the person it means to target.

“Intelligence is never going to be 100 percent accurate,” said Rick “Ozzie” Nelson, director of the Homeland Security and Counterterrorism Program at the Center for Strategic and International Studies in Washington. “The president himself has to decide how much risk he’s willing to take when he approves a strike. You have to consider the possible benefits -- the value of a target -- against the risk.”

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In al-Libi’s case, targeting the Libyan in the Pakistani village of Khassu Khel was worth the risk of missing him, perhaps killing innocent people, and further damaging the frayed U.S. relationship with Pakistan, which condemned the strike, the two US officials said.